A modified UNIQUAC model with linear temperature-dependent parameters is proposed to describe the thermodynamic properties (water activity, osmotic coefficient, vapor pressure, boiling temperature, freezing point and solubility data) of three binary systems : D-glucose/water, D-fructose/water and sucrose/water, New UNIQUAC interaction parameters are presented, estimated using the above mentioned binary data, collected from the literature. Good predictions of vapor-liquid and solid-liquid equilibrium data for ternary and quaternary mixtures of D-glucose, D-fructose, sucrose and water components are obtained. This approach uses the symmetric convention for all the components, pure fused sugar at solution pressure and temperature being its reference state. Therefore, it allows straightforward calculations of solid-liquid equilibria of sugars in mixed solvents. This constitutes an important advance over the approach based on the knowledge of the dilution enthalpy data available in the literature.